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Investigation on Phytochemical Content and Antioxidant Activity of Locally Grown Garlic (allium Sativum L.) in Bangladesh

Al Mamun
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Nazmul Hasan
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Hazrat Belal
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Rokon Ul Karim
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Dobirul Islam
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Sayela Afroz
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Ariful Islam
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Tabassum Ara
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Sirajam Munira
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Masudul Hasan Khan
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Amirul Islam
Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi, Bangladesh

Abstract/ Executive Summary:

Garlic (Allium sativum L.) belonging to the Alliaceae family has played important dietary and medicinal roles throughout the history. The present study was undertaken to investigate the phytochemical content as well as antioxidant activity of local variety garlic extract using different solvent systems in Bangladesh. Five different types of extract were prepared using methanol, ethanol, acetone, chloroform and petroleum ether as solvent. We performed the phytochemical screening and determined the total phenolic, flavonoid, flavonol and proanthocyanidin content of the extracts using standard procedures. Several in vitro assay models were employed to investigate the antioxidant activity. Out of the five extracts, the acetone extract of local variety possessed the highest content of phenolics (110.76±1.9mg of gallic acid equivalent/gm of dry extract)), flavonoids (43.32±2.7mg of catechin equivalent/gm of dry extract), flavonols (15.31±2.3mg of quercetin equivalent/gm of dry extract)) and proanthocyanidins (8.54±0.5 mg of catechin equivalent/gm of dry extract). The radical scavenging activity, the total antioxidant capacity as well as the reducing power of the extracts increased with the increase of concentration. In total antioxidant capacity test and ferric reducing antioxidant power assay acetone extract of local variety showed the highest activity. In DPPH, ABTS, hydroxyl radical scavenging assay and lipid peroxidation inhibition assay strong antioxidant activities were observed by each extract in which acetone extract of local variety was found to be the best one with the IC50 values (in µg/ml) of 5.1±0.9 (DPPH assay), 11.3±0.2 (ABTS assay), 15.7±0.6 (Hydroxyl radical assay) and 19.5±0.3 (Lipid peroxidation assay). Findings of the present study suggested that local variety garlic of Bangladesh is a promising source of natural antioxidant and could have great importance as therapeutic agent in various diseased conditions. The study also recommended that acetone would be the preferable solvent for extracting polyphenols from garlic.

Keywords: Garlic, Phytochemical, Antioxidant activity

Location: Department of Botany, University of Rajshahi, Bangladesh.

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Garlic

Objectives:

The present study was undertaken to investigate the phytochemical content as well as antioxidant activity of local variety garlic extract using different solvent systems in Bangladesh.

Methodology:

For the present study, local variety garlic of Bangladesh was collected from the local area of Rajshahi (north-western part of Bangladesh) and authenticated by the Department of Botany, University of Rajshahi, Bangladesh. The garlic were first washed with water to remove adhering dirt, chopped into small pieces and then shed dried. After complete drying, the entire portions were grinded into a coarse powder by a grinding machine and stored in an airtight container for further use. Five different solvents namely ethanol, methanol, chloroform, acetone and petroleum ether were used for extraction. For each solvent about 100gm of the powdered material was taken in separate clean, round bottomed glass bottle and soaked in 500 ml of solvent. The container with its content was sealed by cotton plug and aluminum foil and kept for a period of 15 days accompanying occasional shaking and stirring. The resulting extracts were filtered through Whatman No. 1 filter paper. Afterwards, the solvents were evaporated under reduced pressure at 39?C using rotary evaporator. Finally, the residues were kept in small sterile bottles under refrigerated conditions until used. Thus, five types of extracts of garlic were obtained as Methanol Extract (MEG), Ethanol Extract (EEG), Chloroform Extract (CEG), Acetone Extract (AEG) and Petroleum ether Extract (PEG). All the chemicals and reagents used throughout this investigation were of reagent grade. Qualitative phytochemical tests were carried out to detect some bioactive components present in the extracts. The main bioactive groups (Polyphenols, Terpenoids, Steroids, Saponins, Tannin, Flavonoids, Alkaloids and Glycosides) were identified in each extract using different standard methods [5] . Total phenolic contents of the extracts were determined by the modified Folin-Ciocalteu method described by Wolfe et al. [6]. An aliquot of the extracts/standard was mixed with 2 ml Folin-Ciocalteu reagent (previously diluted with water 1:10 v/v) and 2 ml (75 g/l) of sodium carbonate. The test tubes were vortexed for 15 seconds and kept for 20 minutes at 25°C for color development. Absorbance was then measured at 760 nm using UV-spectrophotometer (Shimadzu, USA). Total phenolic contents were expressed in terms of gallic acid equivalent, GAE, mg of GA/g of dry extract. Total flavonoids were estimated using the method described by Ordonez et al. [7]. To 0.5 ml of samples/standard, 1.5 ml of methanol, 100 μl of 10% AlCl₃, 100 μl of 1M potassium acetate solution and 2.8 ml of distilled water were added. After 90 minutes of incubation at room temperature (RT), the absorbance was measured at 420 nm. Total flavonoid contents were expressed in terms of catechin equivalent, CAE, mg of CA/g of dry extract. Total flavonols in the plant extracts were estimated using the method of Kumaran and Karunakaran [8]. To 2.0 ml of sample/standard, 2.0 ml of 2% AlCl₃ in ethanol and 3.0 ml (50 g/L) sodium acetate solutions were added. The absorption at 440 nm was read after 2.5 hours at 20°C. Extract/standard was evaluated at a final concentration of 0.1 mg/ml. Total content of flavonols was expressed in terms of quercetin equivalent, QUE, mg of QU/g of dry extract. Determination of content of proanthocyanidins was based on the procedure reported by Sun et al. [9]. A volume of 0.5 ml of 0.1 mg/ml of extracts/standard solution was mixed with 3 ml of 4% vanillin-methanol solution and 1.5 ml hydrochloric acid; the mixture was allowed to stand for 15 minutes. The absorbance was measured at 500 nm. Total content of proanthocyanidins was expressed in terms of catechin equivalent, CAE, mg of CA/g of dry extract. Total antioxidant capacity (TAC) of samples/standard was determined by the method reported by Prieto et al. [10] with some modifications. 0.5 ml of samples/standard at different concentrations was mixed with 3 ml of reaction mixture containing 0.6 M sulphuric acid, 28 mM sodium phosphate and 1% ammonium molybdate into the test tubes. The test tubes were incubated at 95°C for 10 minutes to complete the reaction. The ferric reducing antioxidant capacity of samples/standard was evaluated by the method of Oyaizu [11]. 0.25 ml of samples/standard solution at different concentrations, 0.625 ml of potassium buffer (0.2 M) and 0.625 ml of 1% potassium ferricyanide [K3Fe (CN)6] solution were added into the test tubes. The reaction mixture was incubated for 20 minutes at 50°C to complete the reaction. Then 0.625 ml of 10% TCA solution was added into the test tubes. The total mixture was centrifuged at 3000 rpm for 10 minutes. After that, 1.8 ml supernatant was withdrawn from the test tubes and was mixed with 1.8 ml of distilled water and 0.36 ml of 0.1% FeCl₃ solution. DPPH free radical scavenging activity was determined using the method described by Choi et al. [12]. A solution of 0.1 mM DPPH in methanol was prepared and 2.4 ml of this solution was mixed with 1.6 ml of extractives in methanol at different concentrations. Then percentage DPPH radical scavenging activity was plotted against concentration, and from the graph IC50 was calculated.

Source of Information: International Journal of Biology Research, Volume 1; Issue 5; November 2016; Page No. 37-42

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Achievement/Findings:

The present study suggested that local variety garlic of Bangladesh possesses a wide variety of pharmacologically important compounds and could have great importance as therapeutic agent in the protection against oxidative stress. The study also recommended that acetone would be the preferable solvent for extracting polyphenols from garlic. Further studies are needed to identify the chemical constituents of garlic responsible for antioxidant activity.

Knowledge Management: Journal